1. Field of the Invention
The present invention relates to a process and synergistic composition for dewatering an aqueous mineral slurry and increasing the production of a resulting filter cake. In particular, this invention provides such a process and synergistic composition wherein the aqueous mineral slurry is dewatered by mixing it with an effective amount of a nonionic surfactant and with an effective amount of a cationic polymer, and subjecting the above to a filtration process for removing the water and increasing the production of the resulting filter cake.
2. Background Art
Numerous mineral ores are processed to recover the most valuable components. The ores are processed, for example but not limited to, by crushing, sieving, cycloning, washing, floating and thickening to concentrate the most desired components to form a concentrated aqueous mineral slurry. Components of minerals generally are concentrated by these procedures that are well known by those skilled in the art. Such a concentrated mineral slurry is customarily then subject to a dewatering process in order to achieve liquid water removal from the concentrated mineral slurry. As used herein in the present invention, the term “concentrated mineral slurry” may be for example but not limited to concentrates of iron ores, copper ores, combinations thereof, salts, oxides and sulfides thereof, and in particular, magnetite iron ore. Other examples of a concentrated mineral slurry may contain metals such as molybdenum, nickel, zinc ore, platinum group metals, sand and gravel. As used herein in the present invention, concentrated mineral slurry does not include hematite iron ore or coal. One of the final recovery steps usually involves some form of solid/liquid separation, i.e. filtration or centrifugation. The residual moisture contained in the concentrated mineral ore product can greatly affect subsequent processing of the product such as for example but not limited to pelletizing or smelting or even transportation costs.
Concentrated mineral slurries have been the subject of dewatering processes for many years. The dewatering process endeavors to achieve liquid water removal from the concentrated mineral slurry. A goal of the dewatering process is to decrease the residual liquid water content of the starting mineral slurry concentrate. Dewatering additives such as flocculants in combination with an anionic surfactant have been added to concentrated mineral slurries to reduce the liquid water content of the treated slurry being subjected to filtration. In theory, dewatering aids should increase production rates as well as decrease the amount of water present in the filtered ore or coal cake solids. Because the filtered solids contain less water, the overall production is expected to increase. However, in practice this is not always observed. Employing the additives and additive combinations known to those skilled in the art, not only does the moisture of the filtered solids decrease but the production solids decrease as well when compared to the untreated ore slurry. Traditionally, polymers have been used to agglomerate solids and increase the filtration rate. However, polymers tend to entrain water with the solids and thus cause the moisture content of the ore cake to increase. In many instances, the end use or processing of the coal or metal ore is detrimentally affected by the higher moisture content.
Up to now, an effective process to dewater mineral slurry is viewed as an opportunity to increase solids production by lowering the residual moisture in the product and inferring increased production through better and more rapid filtration. Elimination of the moisture in the filter cake or centrifuge solids increases the amount of mineral or ore solids on a weight percent basis, thereby reducing freight costs required for transport or energy costs for further drying or processing per kilogram of the mineral, coal or ore solids. However, the use of a dewatering aid alone usually results in some production loss of the filter cake when compared to no treatment at all.
Thus, it is known by those skilled in the art that generally when the moisture content of an aqueous mineral slurry concentrate is beneficially reduced by use of certain additives, a disadvantage also occurs in that the production of the resulting filter cake is decreased at the expense of achieving the beneficial dewatering. None of the background art processes have addressed both the need to reduce the residual liquid water content of the concentrated mineral slurry while simultaneously increasing the production of the mineral concentrate filter cake that results from the water removal process such as for example but not limited to a filtration process. The present applicants have developed such a process and synergistic additive combination that advantageously provides for a reduction in the residual liquid water content of the concentrated mineral slurry while also providing for an increased production of the filter cake that results from the water removal process.
U.S. Pat. No. 4,207,186 (Wang et al. '186) provides a process for dewatering mineral and coal concentrates comprising mixing an aqueous slurry of a mineral concentrate and an effective amount of a dewatering aid that is a combination of hydrophobic alcohol having an aliphatic radical of eight to eighteen carbon atoms and a nonionic surfactant of the formula R—(OCH2CH2)xOH wherein x is an integer of 1-15, R is a branched or linear aliphatic radical containing six to twenty-four carbon atoms in the alkyl moiety, and subjecting the treated slurry to filtration. Wang et al. '186 states that when a hydrophobic alcohol such as decyl alcohol is combined with a nonionic surfactant, lower moisture contents are obtained with iron ore concentrate than had a dewatering aid not been employed. Wang et al. '186, however, is unconcerned with increasing the production of the resulting filter cake.
U.S. Pat. No. 4,210,531 (Wang et al. '531) provides a process for dewatering mineral concentrates which consists essentially of first mixing with an aqueous slurry of a mineral concentrate an effective amount of a polyacrylamide flocculant, and next mixing with the flocculant-treated slurry an effective amount of a combination of an anionic surface active agent composition and a water insoluble organic liquid selected from aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic alcohols, aromatic alcohols, aliphatic halides, aromatic halides, vegetable oils and animal oils, wherein the water-insoluble organic liquid being different from any water-insoluble organic liquid present in the anionic surface active agent composition, and thereafter removing the water as a liquid from the slurry. Wang et al. '531, however, does not address and is unconcerned with reducing the residual liquid water content of the concentrated mineral slurry and increasing the production of the resulting filter cake.
The present applicants have found unexpected results with the process of the instant invention in that the present applicants are able to (1) reduce the moisture (liquid water) content of a concentrated mineral slurry that has been treated with their synergistic combination of a nonionic surfactant and cationic polymer, and subjected to a filtration process, and (2) increase the production of the resulting filter cake. Thus, applicants process and synergistic composition combination provides the added economic benefit of increased filter cake production compared to the use of known synergistic combinations of additives that solely reduce the liquid water content of the concentrated mineral slurry. Thus, applicants process and synergistic composition combination fulfills a long-felt but heretofore unmet need in the mineral processing industry.